Method and system for distributed transceivers based on notch filters and passive mixers

ABSTRACT

Aspects of a method and system for a distributed transceiver for high frequency applications may include generating a second signal from a first signal by frequency-translating the first signal via a plurality of conversion stages. Each of the plurality of conversion stages may frequency-translate a corresponding input signal by a local oscillator frequency or by a fraction of said local oscillator frequency, and each of the plurality of conversion stages may comprise a multiplier and a notch filter. The first signal may be the corresponding input signal to an initial stage of a the plurality of conversion stages, an output signal of a previous one of the plurality of conversion stages may be the corresponding input signal to a subsequent one of the plurality of conversion stages, and the second signal may be an output signal of a final stage of the plurality of conversion stages.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to:

-   U.S. application Ser. No. ______ (Attorney Docket No. 18760US01),    filed on even date herewith;-   U.S. application Ser. No. ______ (Attorney Docket No. 18761US01),    filed on even date herewith;-   U.S. application Ser. No. ______ (Attorney Docket No. 18759US01),    filed on even date herewith;-   U.S. application Ser. No. ______ (Attorney Docket No. 18758US01),    filed on even date herewith; and-   U.S. application Ser. No. ______ (Attorney Docket No. 18766US01),    filed on even date herewith.

Each of the above referenced applications is hereby incorporated hereinby reference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to signal processing forcommunication systems. More specifically, certain embodiments of theinvention relate to a method and system for distributed transceiversbased on notch filters and passive mixers.

BACKGROUND OF THE INVENTION

In 2001, the Federal Communications Commission (FCC) designated a largecontiguous block of 7 GHz bandwidth for communications in the 57 GHz to64 GHz spectrum. This frequency band was designated for use on anunlicensed basis, that is, the spectrum is accessible to anyone, subjectto certain basic, technical restrictions such as maximum transmissionpower and certain coexistence mechanisms. The communications takingplace in this band are often referred to as ‘60 GHz communications’.

With respect to the accessibility of this designated portion of thespectrum, 60 GHz communications is similar to other forms of unlicensedspectrum use, for example Wireless LANs or Bluetooth in the 2.4 GHz ISMbands. However, communications at 60 GHz may be significantly differentin aspects other than accessibility. For example, 60 GHz signals mayprovide markedly different communications channel and propagationcharacteristics, at least due to the fact that 60 GHz radiation ispartly absorbed by oxygen in the air, leading to higher attenuation withdistance. On the other hand, since a very large bandwidth of 7 GHz isavailable, very high data rates may be achieved. Among the applicationsfor 60 GHz communications are wireless personal area networks, wirelesshigh-definition television signal, for example from a set top box to adisplay, or Point-to-Point links.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A method and/or system for distributed transceivers based on notchfilters and passive mixers, substantially as shown in and/or describedin connection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating an exemplary wireless communicationsystem, in connection with an embodiment of the invention.

FIG. 2 is a block diagram of an exemplary RF demodulator for ahigh-frequency receiver, in accordance with an embodiment of theinvention.

FIG. 3 is a block diagram of an exemplary RF modulator and demodulatorfor a high-frequency transceiver, in accordance with an embodiment ofthe invention.

FIG. 4 is a flowchart, illustrating an exemplary determination of thedown conversion factors of a demodulator, in accordance with anembodiment of the invention.

FIG. 5 is a diagram of an exemplary demodulator with local oscillatorfrequency mixing, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor distributed transceivers based on notch filters and passive mixers.Aspects of a method and system for distributed transceivers based onnotch filters and passive mixers may comprise generating a second signalfrom a first signal by frequency-translating the first signal via aplurality of conversion stages. Each of the plurality of conversionstages may frequency-translate a corresponding input signal by a localoscillator frequency or by a fraction of said local oscillatorfrequency, and each of the plurality of conversion stages may comprise amultiplier and a notch filter. The first signal may be the correspondinginput signal to an initial stage of a the plurality of conversionstages, an output signal of a previous one of the plurality ofconversion stages may be the corresponding input signal to a subsequentone of the plurality of conversion stages, and the second signal may bean output signal of a final stage of the plurality of conversion stages.

The plurality of conversion stages may be communicatively coupled in acascade configuration. The first signal may be a radio frequency signalor an intermediate frequency signal and the second signal may be abaseband signal. The first signal may be a radio frequency signal or abaseband signal and the second signal may be an intermediate frequencysignal. The first signal may be a baseband signal or an intermediatefrequency signal and the second signal may be a radio frequency signal.A fractional local oscillator signal associated with the fractionallocal oscillator frequency may be generated from a local oscillatorsignal by using one or more frequency dividers. Mixing a localoscillator and/or one or more mixing signals may generate a fractionallocal oscillator signal associated with the local oscillator frequency.The one or more mixing signals may be generated by dividing the localoscillator signal via one or more frequency dividers. A local oscillatormay be a sinusoidal signal with a frequency equal to the localoscillator frequency.

FIG. 1 is a diagram illustrating an exemplary wireless communicationsystem, in connection with an embodiment of the invention. Referring toFIG. 1, there is shown an access point 112 b, a computer 110 a, aheadset 114 a, a router 130, the Internet 132 and a web server 134. Thecomputer or host device 110 a may comprise a wireless radio 111 a, ashort-range radio 111 b, a host processor 111 c, and a host memory 111d. There is also shown a wireless connection between the wireless radio111 a and the access point 112 b, and a short-range wireless connectionbetween the short-range radio 111 b and the headset 114 a.

Frequently, computing and communication devices may comprise hardwareand software to communicate using multiple wireless communicationstandards. The wireless radio 111 a may be compliant with a mobilecommunications standard, for example. There may be instances when thewireless radio 111 a and the short-range radio 111 b may be activeconcurrently. For example, it may be desirable for a user of thecomputer or host device 110 a to access the Internet 132 in order toconsume streaming content from the Web server 134. Accordingly, the usermay establish a wireless connection between the computer 110 a and theaccess point 112 b. Once this connection is established, the streamingcontent from the Web server 134 may be received via the router 130, theaccess point 112 b, and the wireless connection, and consumed by thecomputer or host device 110 a.

It may be further desirable for the user of the computer 110 a to listento an audio portion of the streaming content on the headset 114 a.Accordingly, the user of the computer 110 a may establish a short-rangewireless connection with the headset 114 a. Once the short-rangewireless connection is established, and with suitable configurations onthe computer enabled, the audio portion of the streaming content may beconsumed by the headset 114 a. In instances where such advancedcommunication systems are integrated or located within the host device110 a, the radio frequency (RF) generation may support fast-switching toenable support of multiple communication standards and/or advancedwideband systems like, for example, Ultrawideband (UWB) radio. Otherapplications of short-range communications may be wirelessHigh-Definition TV (W-HDTV), from a set top box to a video display, forexample. W-HDTV may require high data rates that may be achieved withlarge bandwidth communication technologies, for example UWB and/or60-GHz communications.

FIG. 2 is a block diagram of an exemplary RF demodulator for ahigh-frequency receiver, in accordance with an embodiment of theinvention. Referring to FIG. 2, there is shown a demodulator 200comprising an amplifier 202, an RF block 254, a gm FET 256, and aplurality of down conversion stages, of which down conversion stages204, 206 and 208 are illustrated. The down conversion stage 204 maycomprise a multiplier FET 210 a and a filter 212 a. The down conversionstage 206 may comprise a multiplier FET 210 b, a filter 212 b and afrequency divider 214 b. The down conversion stage 208 may comprise amultiplier FET 210 c, a filter 212 c and a frequency divider 214 c. Thefilters 212 a, 212 b, 212 c may comprise suitable circuitry, logicand/or code that may enable notch filtering. In accordance with anembodiment of the invention illustrated in FIG. 2, the filter 212 a, 212b, 212 c may comprise an inductor 250 a, 250 b, 250 c and a capacitor252 a, 252 b, 252 c, respectively. The capacitors 252 a, 252 b, 252 cmay be of variable capacitance and the inductors 252 a, 252 b, 252 c maybe variable, in some instances. There is also shown a received signalr₀(f₀,t)=r₀ that may be a function of a carrier frequency f₀ and time t.The indices for frequency and time may be dropped for illustrativepurposes. Similarly, there is shown r₁,r₂,r_(K),r_(a),r_(b). A localoscillator signal c_(LO)(f_(LO),t)=c_(LO) and a number of frequencyterms

${\frac{f_{LO}}{N_{1}},{\frac{f_{LO}}{N_{1}N_{2}}\mspace{14mu} {and}}}\mspace{14mu} \frac{f_{LO}}{\prod\limits_{k = 1}^{K}N_{k}}$

may be shown, which may illustrate various signals generated byfrequency dividing the local oscillator (LO) signal c_(LO). There isalso shown a supply voltage Vcc.

The amplifier 202 may comprise suitable logic, circuitry and/or codethat may be enabled to amplify a high-frequency RF signal at its input.The gm FET 256 may be enabled to act as an input stage and may convertan input signal to a current and may act as a current source, in someinstances. The RF blocker 254 may be enabled to isolate the RF signalsat the gm FET 256 from the supply voltage Vcc. As illustrated in FIG. 2,the RF blocker may be a inductor, with a high Q factor, in someinstances. In another embodiment of the invention, the RF blocker 254may be a microstrip. The down conversion stages 204, 206 and 208 may besubstantially similar and may comprise suitable logic, circuitry and/orcode that may be enabled to down convert an input signal that may bemodulated onto an RF carrier signal to an output signal that may besimilar to the input signal but modulated onto lower frequency carriersignal. The multiplier FETs 210 a, 210 b and 210 c may be enabled tomultiply two RF input signals and generate an RF output signal that maybe proportional to the product of its input signals. For example, themultiplier FET 210 a may multiply the input signal at its drain terminaland the input signal at its gate terminal to generate an output signalat its source terminal. The filters 212 a, 212 b, 212 c may comprisesuitable logic, circuitry and/or code that may be enabled to attenuate aportion of the frequency spectrum of an input signal. As illustrated inFIG. 2, the filters 212 a, 212 b, 212 c may comprise an inductor 250 a,250 b, 250 c and a capacitor 252 a, 252 b, 252 c, respectively and beenabled to function as notch filters. In some instances, the filters 212a, 212 b, 212 c may be implemented using microstrips. The frequencydividers 214 b and 214 c may comprise suitable logic, circuitry and/orcode that may be enabled to generate an output signal that may besimilar to its input signal, divided in frequency. The frequencydividers may be implemented using Direct Digital Frequency Synthesis orinteger (Miller) dividers, for example.

With reference to FIG. 2, there is shown a demodulator 200 that may bepart of a high-frequency radio frequency receiver. An exemplaryhigh-frequency received signal may ber₀(f₀,t)=s(t)cos(2πf₀t)=s(t)cos(w₀t), where f₀ may be the carrierfrequency and 2πf₀=w₀ may be the corresponding angular frequency. Thesignal s(t) may be, for example, the information-bearing baseband signalthat may be modulated onto the carrier cos(w₀t). In this instance,r₀(f₀,t) may be an in-phase bandpass signal component and a similarblock diagram as illustrated for demodulator 200 may also be used for ademodulator of a quadrature bandpass signal component. In someinstances, the received signal r₀ may be at a high carrier frequency,for example, f₀=60 GHz. In these instances, it may be difficult togenerate a local oscillator signal c_(LO), for example with aPhase-locked loop (PLL), sufficiently high in frequency to achievedemodulation to baseband or, in some instances, to an intermediatefrequency. In addition, high frequency LO signals may generally beundesirable for distribution in a system since the signal transport overconductors may result in transmission line problems, due to the LOsignal's high frequency content. Hence, it may be desirable to generatethe high frequency signal for demodulation of the RF signal in proximityto the received high frequency signal r₀(f₀,t). In these instances, itmay be desirable to generate a local oscillator signal c_(LO) that maybe significantly lower in frequency, for example, f_(LO)=20 GHz, thanthe carrier of the received signal at, for example f₀=60 GHz. Inaccordance with various embodiments of the invention, a plurality ofconversion stages, for example down conversion stages 204, 206 and 208may then be used to down convert the received signal r₀ to basebandand/or intermediate frequency.

An exemplary received signal r₀ may be amplified by a factor z in theamplifier 202 to generate a signal at the input to the multiplier 210 a,given by r′₀(f₀,t)=z·r₀(f₀,t)=z·s(t)cos(w₀t). The multiplier FET 210 amay multiply the signals r′₀ with the local oscillator signalc_(LO)=cos(w_(LO)t), to generate r_(a) according to the followingrelationship, approximately:

$\begin{matrix}\begin{matrix}{r_{a} = {{{r_{0}^{\prime}\left( {f_{0},t} \right)}{c_{LO}\left( {f_{0},t} \right)}} = {{z \cdot {s(t)}}{\cos \left( {w_{0}t} \right)}{\cos \left( {w_{LO}t} \right)}}}} \\{= {\frac{z}{2} \cdot {{s(t)}\left\lbrack {{\cos \left( {{w_{0}t} + {w_{LO}t}} \right)} + {\cos \left( {{w_{0}t} - {w_{LO}t}} \right)}} \right\rbrack}}}\end{matrix} & \;\end{matrix}$

Hence, as may be seen from the above equation, the signal r_(a) maycomprise a sum and a difference term at frequencies determined by thedifference of the carrier frequency w₀ and the local oscillatorfrequency w_(LO). In this instance, in accordance with an embodiment ofthe invention, it may be desirable to demodulate the received signal r₀and hence it may be desirable to retain only the lower frequencycomponent, modulated onto a carrier at frequency w_(c)-w_(LO). This maybe achieved by the filter 212 a, which may reject the higher of thefrequency terms to generate r₁, given by the following relationship:

$r_{1} = {{B\; P\; {F_{212a}\left( r_{a} \right)}} = {\frac{z}{2}{{s(t)}\left\lbrack {\cos \left( {{w_{0}t} - {w_{LO}t}} \right)} \right\rbrack}}}$

In an additional down conversion stage, for example down conversionstage 206, the generated signal r₁ may be down converted further. Thismay be achieved in a similar manner by down converting r₁ with afrequency-divided local oscillator signal. Specifically, as illustratedin FIG. 2, the down converted output signal r₁ from down conversionstage 204 may be multiplied with a signal that may be a frequencydivided version of the local oscillator at the output of the frequencydivider 214 b, namely

$c_{{LO}/N_{1}} = {{\cos \left( {\frac{w_{LO}}{N_{1}}t} \right)}.}$

The divisor, N₁, applied in frequency divider 214 b may be arbitrary. Inmany instances, it may be desirable to choose N₁ a rational number or aninteger. A signal r_(b) may be generated at the output of multiplier 210b that may be given by the following relationship:

$\begin{matrix}\begin{matrix}{r_{b} = {{r_{1} \cdot c_{{LO}/N_{1}}} = {\frac{z}{2}{{s(t)}\left\lbrack {\cos \left( {{w_{0}t} - {w_{LO}t}} \right)} \right\rbrack}{\cos \left( {\frac{w_{LO}}{N_{1}}t} \right)}}}} \\{= {\frac{z}{4}{{s(t)}\left\lbrack {{\cos \left( {{w_{0}t} - {w_{LO}t} + {\frac{w_{LO}}{N_{1}}t}} \right)} + {\cos \left( {{w_{0}t} - {w_{LO}t} - {\frac{w_{LO}}{N_{1}}t}} \right)}} \right\rbrack}}}\end{matrix} & (1)\end{matrix}$

Similar to generating r₁, r₂ at the output of the down conversion stage206 may be generated by applying suitable filtering to r_(b), which mayremove the higher frequency component in filter 212 b, to obtain:

$r_{2} = {\frac{z}{4}{s(t)}{\cos \left( {{w_{0}t} - {w_{LO}t} - {\frac{w_{LO}}{N_{1}}t}} \right)}}$

Further down modulating may be achieved by applying further downconversion stages similar to down conversion stage 206, for example. Asillustrated in FIG. 2, it may be desirable to use a cascade of K downconversion stages. In this case, the output signal r_(K) after K downconversion stages may be given, for example, by the followingrelationship:

$\begin{matrix}{r_{K} = {\frac{z}{2^{K}}{s(t)}{\cos\left( {{w_{0}t} - {{w_{LO}\left( {1 + {\sum\limits_{k = 1}^{K - 1}\frac{1}{\prod\limits_{n = 1}^{k}N_{n}}}} \right)}t}} \right)}}} & (2)\end{matrix}$

In these instances, it may be that the filters in the down conversionstages, for example filters 212 a, 212 b, 212 c may be filtering inorder to attenuate the higher frequency component at their input. Inthis instance, N_(k)>0 ∀k ε 1,2, . . . K−1.

In some instances and for some down conversion stages, it may bedesirable to choose to retain the higher frequency component rather thanthe lower frequency component of the output signal of the multiplier, inorder to get a desirable output at the filter. For example, inaccordance with various embodiments of the invention, the higherfrequency component in r_(b), equation (1), for example, may be retainedby appropriately filtering r_(b) in filter 212 b. In this instance, fromequation (1), r₂ may be given by the following relationship:

$\begin{matrix}{r_{2} = {\frac{z}{4}{s(t)}{\cos \left( {{w_{0}t} - {w_{LO}t} + {\frac{w_{LO}}{N_{1}}t}} \right)}}} & (3)\end{matrix}$

In a general case, either the higher or the lower frequency componentmay be selected for each down conversion stage. As illustrated inequation (3), this may result in the sign of the frequency termcorresponding to a particular down conversion stage to change. Hence,for K down conversion stages, the output r_(K) may be described byequation (2), wherein the coefficients N_(k) may be positive ornegative, as appropriate.

In one embodiment of the invention, the divisors N_(k) may be chosenequal, so that N_(k)=N ∀k. In these instances, equation (2) may be givenby the following relationship:

$\begin{matrix}{r_{K} = {\frac{z}{2^{K}}{s(t)}{\cos \left( {{w_{0}t} - {w_{LO}t{\sum\limits_{k = 0}^{K - 1}\left( \frac{1}{N} \right)^{k}}}} \right)}}} & (4)\end{matrix}$

By choosing z=2^(K), which may be achieved, for example, by amplifyingby a factor of two at each down conversion stage, it may be observedthat the expression in equation (4) may be stable and converge for anarbitrary number of stages when |1/N|<1, so that the limit of (4) may begiven by the following relationship:

$\begin{matrix}{\mspace{20mu} {{{r_{K}_{z = 2^{K}}} = {{s(t)}{\cos \left( {{w_{0}t} - {w_{LO}t{\sum\limits_{k = 0}^{K - 1}\left( \frac{1}{N} \right)^{k}}}} \right)}}}{{r_{K}_{z = 2^{K}}{{\overset{K->\infty}{}{s(t)}}{\cos \left( {{w_{0}t} - \frac{w_{LO}t}{1 - {1/N}}} \right)}}} = {{s(t)}{\cos \left( {{w_{0}t} - \frac{{N \cdot w_{LO}}t}{N - 1}} \right)}}}}} & (5)\end{matrix}$

where equation (5) may converge more rapidly for larger N. For example,if N=4, the frequency term in equation (5) may converge to w₀t−1.3·w_(LO)t as K→∞. However, as may be observed from the first line ofequation (5), with K=3, the frequency term may already bew₀t−1.3125˜w_(LO)t and hence the frequency correction term may beapproximately

$\frac{1.3125}{1.\overset{\_}{3}} = {{63/64} \approx {98.5\%}}$

of the desired frequency correction term.

In accordance with various embodiments of the invention, the number ofdown conversion stages may be arbitrary. Moreover, in some instances, itmay be desirable that the first down conversion stage, for example downconversion stage 204 may comprise a frequency divider, similar, forexample, to down conversion stage 206 and/or down conversion stage 208.The number of down conversion stages K may be determined, for example,based on the difference between w₀ and w_(LO), and the desiredintermediate frequencies. In some instances, it may be possible that thedivisors may be software-programmable. Moreover, the structureillustrated in FIG. 2 may be used by a modulator, whereby the sum termsinstead of the difference terms may be retained in order to obtain anoutput signal at a higher frequency that the input signal. For example,in equation (1), the higher frequency component may be retained by thefilter 212 b in the down conversion stage 206, whereby the downconversion stage 206 may effectively become an up conversion stage, asillustrated in equation (3).

FIG. 3 is a block diagram of an exemplary RF modulator and demodulatorfor a high-frequency transceiver, in accordance with an embodiment ofthe invention. Referring to FIG. 3, there is shown amodulator/demodulator system 300 comprising a demodulator 320 and amodulator 330. The demodulator 320 may be substantially similar to thedemodulator 200 illustrated in FIG. 2. The elements of demodulator 320may be similar to their corresponding elements in demodulator 200.Specifically, elements 302, 304, 306, 308, 310 a, 310 b and 310 c, 312a, 312 b, and 312 c, 314 b and 314 c, 350 a, 350 b and 350 c and 352 a,352 b and 352 c may be similar to elements 202, 204, 206, 208, 210 a,210 b and 210 c, 212 a, 212 b, and 212 c, 214 b and 214 c, 250 a, 250 band 250 c and 252 a, 252 b and 252 c, respectively.

The modulator 330 may comprise an amplifier 302 a, an AC blocker 354 a,a gm FET 356 a, and a plurality of up conversion stages, of which upconversion stages 304 a, 306 a and 308 a may be illustrated. Themodulator 330 may comprise suitable logic, circuitry and/or code thatmay be enabled to modulate an input signal, r_(T0), to radio frequency,r_(TK). The sub-script ‘T’ may indicate a transmit signal associatedwith the modulator 330. The up conversion stage 304 a, 306 a and 308 amay comprise filters 312 d, 312 e and 312 f and multiplier FETs 310 d,310 e and 310 f, respectively. The filters are similar to the filters312 a, 312 b and 312 c. There is also shown a transmit signalr_(T0)(f_(T0),t)=r_(T0) that may be a function of frequency f_(T0) andtime t. The indices for frequency and time may be dropped forillustrative purposes. Similarly, there is shownr_(T1),r_(T(K−1)),r_(TK), which may be the output signals of upconversion stages 1, (K−1) and K, respectively.

The functionality of the modulator 330 may be considered similar to thedemodulator 320 functionality in reverse. In particular, whereas in thedemodulator 320, the input signal r₀ may be a signal modulated onto aradio frequency carrier or an intermediate frequency carrier forfrequency translation to a lower frequency, the input signal of themodulator 330 may be a baseband signal or an intermediate frequencysignal for frequency translation to a higher frequency, for example tointermediate frequency or radio frequency, respectively. However, thefrequency up conversion may be achieved similarly to the frequency downconversion. The main difference may be found in the filtering, whereinthe higher frequency components may be retained, as described forequation (3) and FIG. 2. For example, in up conversion stage 308 a, theoutput signal r_(T1) may be given by the following relationship:

$\begin{matrix}\begin{matrix}{r_{Ta} = {{r_{T\; 0} \cdot c_{{LO}/{({N_{1} \cdot N_{2} \cdot \mspace{11mu} \ldots \mspace{11mu} \cdot N_{K - 1}})}}} = {{{x(t)}\left\lbrack {\cos \left( {w_{T\; 0}t} \right)} \right\rbrack}{\cos\left( {\frac{w_{LO}}{\prod\limits_{k = 1}^{K - 1}N_{k}}t} \right)}}}} \\{= {\frac{1}{2}{{x(t)}\left\lbrack {{\cos\left( {{w_{T\; 0}t} - {\frac{w_{LO}}{\prod\limits_{k = 1}^{K - 1}N_{k}}t}} \right)} + {\cos\left( {{w_{T\; 0}t} + {\frac{w_{LO}}{\prod\limits_{k = 1}^{K - 1}N_{k}}t}} \right)}} \right\rbrack}}}\end{matrix} & (6)\end{matrix}$

where w_(T0)=2πf_(T0) may be the angular frequency of the input signalr_(T0)=x(t)cos(w_(T0)t), wherein x(t) may be the information bearingbaseband signal, similar to s(t)for the received signal. For an upconversion stage, for example up conversion stage 308 a, the filter 312f may maintain, for example, the higher of the frequency components ofr_(Ta) from equation (6), so that r_(T1) may be given by the followingrelationship:

$\begin{matrix}{r_{T\; 1} = {{B\; P\; {F_{312f}\left( r_{Ta} \right)}} = {\frac{1}{2}{x(t)}{\cos\left( {{w_{T\; 0}t} + {\frac{w_{LO}}{\prod\limits_{k = 1}^{K - 1}N_{k}}t}} \right)}}}} & (7)\end{matrix}$

Similar to FIG. 2, the filter 312 f may be an arbitrary filter and mayretain, for example, the lower and/or higher frequency componentscomprised in its input signal, and may not be limited to the expressionprovided in equation (7).

In accordance with an embodiment of the invention, the modulator 330 mayshare the frequency dividers, for example frequency dividers 314 b and314 c, with the demodulator 320, the modulator 330 may be configured ina manner that may provide the same up conversion frequency steps thatmay be provided in the down conversion. In particular, if the filter ina down conversion stage may retain the lower frequency component, byretaining the higher frequency component in the corresponding upconversion stage, the up conversion signal may be upconverted infrequency by the same amount as a down conversion signal may bedownconverted in frequency by the corresponding down conversion stage.For example, as described for FIG. 2, the received signal r₀ may be downconverted from angular frequency w₀ to w₁=w₀−w_(LO) for signal r₁ indown conversion stage 304. Similarly, the signal r_(T(K−1)) at angularfrequency w_(T(K−1)) may be converted by the corresponding up conversionstage 304 a to angular frequency w_(TK)=w_(T(K−1))+w_(LO). Hence, byappropriately choosing the filters in both the demodulator 320 and themodulator 330, the frequency translation across the entire modulator maybe chosen approximately equal across the entire demodulator, forexample, in opposite directions. In one exemplary embodiment of theinvention, the received signal r₀, for example, may be down converted by40 GHz from r₀ to r_(K), and the transmit signal r_(T0) may be upconverted by 40 GHz from at r_(T0) to r_(TK).

FIG. 4 is a flowchart, illustrating an exemplary determination of thedown conversion factors of a demodulator, in accordance with anembodiment of the invention. In accordance with the description for FIG.2 and FIG. 3, it is understood by one skilled in the art that there area large number of approaches that may be chosen to determine a number offrequency conversion stages and appropriate frequency conversionfactors. With reference to FIG. 4, there is shown one approach that maybe used to determine a number of frequency conversion stages and theassociated conversion factors and/or divisors.

In accordance with an exemplary embodiment of the invention,determination of a down conversion system, for example a demodulatorsimilar to FIG. 2, may be illustrated in FIG. 4. Initially, in step 404,a reduction factor may be determined. The reduction factor, for examplex, may be determined by the difference between the frequency of thecarrier of the received signal, w₀, and the desired carrier frequency atthe output of the demodulator, w_(K). The reduction factor may beexpressed in terms of local oscillator frequency, as given by thefollowing relationship:

$x = \frac{w_{0} - w_{K}}{w_{LO}}$

Based on the reduction factor, the number of stages according to thisexemplary approach may be determined as given by the followingrelationship, in step 406:

K=┌x┐

where the operation ┌.┐ may denote ‘the nearest greater integer’. Inthis instance, for K conversion stages, K−1 conversion stages may bechosen such that N_(k)=1 ∀k ε 0,1, . . . K−1. The down conversion factorN_(K) of the K-th down conversion stage may correspondingly be chosen,in step 408, as 0<N_(K)<1 and may be given by the followingrelationship:

$N_{K} \approx \frac{1}{x - \left\lfloor x \right\rfloor}$

where the operation └.┘ may denote ‘the nearest smaller integer’, andthe operation ‘≈’ may be interpreted as ‘a sufficiently close rationalnumber’, in accordance with the accuracy that may be required in thesystem.

In an exemplary embodiment of the invention, in instances where w₀ maybe 60 GHz, the target frequency w_(K) may be 1 GHz, and the localoscillator frequency w_(LO) may be 8 GHz, x=7.375. Hence, it may bedesirable to use K=8 stages. Hence,

${N_{k} = {1{\forall{k \in 0}}}},1,{{\ldots \mspace{11mu} 6\mspace{14mu} {and}\mspace{14mu} N_{K}} = {0.375 = {\frac{3}{8}.}}}$

FIG. 5 is a diagram of an exemplary demodulator with local oscillatorfrequency mixing, in accordance with an embodiment of the invention.Referring to FIG. 5, there is shown a demodulation system 500 comprisingan amplifier 502, an RF blocker 554, a gm FET 556, and down conversionstages 504, 506 and 508, an LO mixer 520 and a fractional LO cascade530. The down conversion stages 504, 506 and 508 may comprise multiplierFETs 510 a, 510 b and 510 c and filters 512 a, 512 b and 512 c,respectively. The down conversion stages 504, 506 and 508 may besubstantially similar to the down conversion stages in FIG. 2, forexample 204, 206 and 208. The filters 512 a, 512 b and 512 c may besimilar to the filters 212 a, 212 b, 212 c, for example, and maycomprise inductors and capacitors or microstrips, as described for FIG.2. The LO mixer 520 may comprise filters 512 d and 512 e and multipliers510 d and 510 e. The fractional LO cascade 530 may comprise frequencydividers 514 a, 514 b and 514 c. There is also shown a received signalr₀(f₀,t)=r₀ that may be a function of a receive carrier frequency f₀ andtime t. The indices for frequency and time may be dropped forillustrative purposes. Similarly, there is shownr₁,r₂,r₃,r_(a),r_(b),r_(c),r_(m1),r_(m2),r_(m3). A local oscillatorsignal c_(LO)(f_(LO),t)=c_(LO) may be shown and a number of frequencyterms

${\frac{f_{LO}}{N_{1}},{\frac{f_{LO}}{N_{1}N_{2}}\mspace{14mu} {and}}}\mspace{14mu} {\frac{f_{LO}}{\prod\limits_{k = 1}^{K}N_{k}},}$

which may illustrate various signals generated by frequency dividing thelocal oscillator (LO) signal c_(LO), for example,c_(LO)(f_(LO)/N,t),c_(LO)(f_(LO)/N²,t) and c_(LO)(f_(LO)/N³,t).

In some instances, the type of frequency divider, for example 214 b and214 c, may be constrained due to a particular implementation. Forexample, it may be possible that N_(k) ε□⁺. In this regard, the divisorsmay be chosen only from among the set of positive integers. In anotherembodiment of the invention illustrated in FIG. 5, the frequency dividermay be more constrained and N_(k)=N ∀k, for example. Notwithstanding, inaccordance with an embodiment of the invention, high precision may beachieved even for fixed N_(k)=N, in some instances at the expense of anLO mixer 520. For example, when N=N_(k)=2 ∀k, from equation (5), forexample, one may see that the frequency term may converge to

${K->{{\infty \text{:}\mspace{14mu} w_{0}t} - {{\frac{N}{N - 1} \cdot w_{LO}}t}}} = {{w_{0}t} - {2w_{LO}{t.}}}$

For different number of stages K, it may be seen from the followingtable how the term correction term

$\frac{N}{N - 1}$

may converge:

K ${Correction}\mspace{14mu} {term}\mspace{11mu} \frac{N}{N - 1}$Error termw.r.tK = ∞ (in %) Differencebetweenadjacent stages 0 1 50 1 11.5 25 0.5 2 1.75 12.5 0.25 3 1.875 6.25 0.125 4 1.9375 3.125 0.0625 51.96875 1.5625 0.03125 6 1.984375 0.78125 0.015625 7 1.992188 0.3906250.007813 8 1.996094 0.195313 0.003906 9 1.998047 0.097656 0.001953 101.999023 0.048828 0.000977Hence, as may be seen from the above second column, by increasing thenumber of down conversion stages, the correction term may be chosenarbitrarily close to 2, as may be seen from column 3 of the above table.For example, for K=2, a 12.5% error with respect to K=∞ may be obtained.Hence, in cases where the correction term

$\frac{N}{N - 1}$

may be chosen as an integer greater or equal to 2, arbitrary accuracymay be achieved easily. For example in the system illustrated in FIG. 2,to approximate a correction factor of 5=3+2, stages N_(k)=1;k ε 0,1,2,to obtain the factor 3, followed by an arbitrary number of stages withN_(k)=2 ∀k: k>2, to get arbitrarily close to 5.

In order to generate arbitrary frequency correction terms based on afixed divisor factor N_(k)=N ∀k, an LO mixer 520 may be used togetherwith the fractional LO cascade 530. The fractional LO cascade 530 maycomprise suitable logic, circuitry and/or code that may be enabled toaccept a local oscillator input signal c_(LO)(f_(LO),t) and frequencydivide it in a cascade of frequency dividers, for example 514 a, 514 band 514 c, to generate fractional local oscillator signals, for examplec_(LO)(f_(LO)/N,t),c_(LO)(f_(LO)/N²,t) and c_(LO)(f_(LO)/N³,t),respectively. By appropriately mixing these fractional local oscillatorsignals, small frequency differences may be generated that may be usedin the down conversion stages. The resolution, or frequency steps,obtainable may depend on the number of frequency dividers in thefractional LO cascade 530. For example, the exemplary embodimentillustrated in FIG. 5 may comprise 3 frequency dividers 514 a, 514 b and514 c and N=2 may be set. By appropriately multiplying and filteringvarious fractional LO terms obtained in the fractional LO cascade 530 inthe LO mixer 520, arbitrary down conversion factors may be achieved inthe down conversion stages, for a sufficient number of frequencydividers in the LO cascade 530.

For example, the exemplary embodiment illustrated in FIG. 5 may resultin an overall down conversion factor of 4.125, that is, r₃ ∝cos(w₀t−4.125w_(LO)t). In the LO mixer 520, the multiplier 510 d may becommunicatively coupled to c_(LO), and the output of the multiplier 510d may be given by the following relationship:

${c_{LO} \cdot c_{LO}} = {{\cos^{2}\left( {w_{LO}t} \right)} = {\frac{1}{2}\left\lbrack {{\cos \left( {2w_{LO}t} \right)} + 1} \right\rbrack}}$

Similar to the filtering described for FIG. 2, the filter 512 d mayretain the low-frequency or high frequency component. In this particularinstance, the filter 512 d may retain the high-frequency component andgenerate, at its output a signal r_(m1), given by the followingrelationship:

$r_{m\; 1} = {{B\; P\; F_{512d}} = {\frac{1}{2}{\cos \left( {2w_{LO}t} \right)}}}$

The signal r_(m1) may be communicatively coupled to the multiplier 510 ain the down conversion stage 504. Similarly, the output of frequencydivider 514 b may be coupled to the input of the multiplier 510 b, sothat

$r_{m\; 2} = {{c_{LO}\left( {\frac{w_{LO}}{N^{2}},t} \right)}.}$

It may be observed from FIG. 5 that the output of frequency divider 514b may be directly coupled to the down conversion stage 506 and may notbe mixed beforehand in the LO mixer 520. Similarly, it may be observedthat the output of the frequency divider 514 a may not be coupled to theLO mixer 520 or a down conversion stage, in this embodiment of theinvention. Instead, the output of frequency divider 514 a may be used asthe input to the frequency divider 514 b.

The output of the frequency divider 514 c may be communicatively coupledto an input of the multiplier 510 e. The second input of the multiplier510 e may be coupled to the output of the filter 512 d. Hence, theoutput of the multiplier 510 e in the LO mixer may be described by thefollowing relationship:

$\begin{matrix}{{c_{{LO}/N^{3}} \cdot r_{m\; 1}} = {\frac{1}{2}{\cos \left( {2w_{LO}t} \right)}{\cos \left( {\frac{w_{LO}}{N^{3}}t} \right)}}} \\{= {\frac{1}{4}\left\lbrack {{\cos \left( {{2w_{LO}t} + {\frac{w_{LO}}{N^{3}}t}} \right)} + {\cos \left( {{2w_{LO}t} - {\frac{w_{LO}}{N^{3}}t}} \right)}} \right\rbrack}}\end{matrix}$

By retaining the lower frequency component from the output signal of 510e in the filter 512 e, the output signal of the filter 512 e may begiven by the following relationship:

$\begin{matrix}{r_{m\; 3} = {{B\; P\; {F_{512e}\left( {c_{{LO}/N^{3}} \cdot r_{m\; 1}} \right)}} = {\frac{1}{4}{\cos \left( {{2w_{LO}t} - {\frac{w_{LO}}{8}t}} \right)}}}} \\{= {\frac{1}{4}{\cos \left( {1.875w_{LO}t} \right)}}}\end{matrix}$

In the down conversion stage 504, the output signal r₁ may be given bythe following relationship:

$r_{1} = {{B\; P\; {F_{512a}\left( {z\; r_{0}r_{m\; 1}} \right)}} = {\frac{z}{4}{s(t)}{\cos \left( {{w_{0}t} - {2w_{LO}t}} \right)}}}$

where the filter 512 a may be chosen to retain the lower frequencycomponent and r₀=s(t)cos(w₀t). z may be the amplification factorintroduced by amplifier 502, similar to the description for FIG. 2.Correspondingly, the output of the down conversion stage 506 may begiven by the following relationship:

$r_{2} = {{B\; P\; {F_{512b}\left( {r_{1}r_{m\; 2}} \right)}} = {\frac{z}{8}{s(t)}{\cos \left( {{w_{0}t} - {2w_{LO}t} - \frac{w_{LO}t}{4}} \right)}}}$

where the filter 512 b may have retained the lower frequency component.The output of the down conversion stage 508 may be given by thefollowing relationship:

$r_{3} = {{B\; P\; {F_{512c}\left( {r_{2}r_{m\; 3}} \right)}} = {\frac{z}{64}{s(t)}{\cos \left( {{w_{0}t} - {2w_{LO}t} - \frac{w_{LO}t}{4} - {1.875w_{LO}t}} \right)}}}$  r₃_(z = 64) = s(t)cos (w₀t − 4.125w_(LO)t)

Hence, as described above, the output signal r₃ that may be generated bythe down conversion stages, may be frequency translated by a factor of4.125. By appropriately choosing the number of frequency dividers in thefractional LO cascade 530 and suitably combining the outputs of thefrequency dividers in the LO mixer 520, an arbitrary down conversion(frequency translation) factor may be achieved. In various embodimentsof the invention, a similar approach may be used for a modulator byappropriate filtering in the conversion stages 504, 506 and 508, asdescribed above and with respect to FIG. 2.

In accordance with an embodiment of the invention, a method and systemfor distributed transceivers based on notch filters and passive mixersmay comprise generating a second signal from a first signal for exampler_(K), by frequency-translating the first signal, for example r₀, via aplurality of conversion stages, as illustrated in FIG. 2, FIG. 3 andFIG. 5. Each of the plurality of conversion stages, for exampleconversion stages 204, 206 and 208, may frequency-translate acorresponding input signal by a local oscillator frequency or by afraction of said local oscillator frequency, and each of the pluralityof conversion stages may comprise a multiplier and a notch filter, asdescribed for FIG. 2. The first signal may be the corresponding inputsignal to an initial stage of a the plurality of conversion stages, anoutput signal of a previous one of the plurality of conversion stagesmay be the corresponding input signal to a subsequent one of theplurality of conversion stages, and the second signal may be an outputsignal of a final stage of the plurality of conversion stages.

The plurality of conversion stages may be communicatively coupled in acascade configuration, as illustrated in FIG. 5. The first signal may bea radio frequency signal or an intermediate frequency signal and thesecond signal may be a baseband signal. The first signal may be a radiofrequency signal or a baseband signal and the second signal may be anintermediate frequency signal. The first signal may be a baseband signalor an intermediate frequency signal and the second signal may be a radiofrequency signal, as described for FIG. 2. A fractional local oscillatorsignal, for example C_(LO/N), associated with the fractional localoscillator frequency, for example W_(LO)/N, may be generated from alocal oscillator signal, for example c_(LO) by using one or morefrequency dividers, for example 514 a, 514 b. Mixing a local oscillator,for example c_(LO), and/or one or more mixing signals may generate afractional local oscillator signal associated with the local oscillatorfrequency, as described for FIG. 2. The one or more mixing signals maybe generated by dividing the local oscillator signal via one or morefrequency dividers, as illustrated in FIG. 5. A local oscillator may bea sinusoidal signal with a frequency equal to the local oscillatorfrequency. The notch filter may comprise one or more inductors and oneor more capacitors, or one or more microstrips.

Another embodiment of the invention may provide a machine-readablestorage, having stored thereon, a computer program having at least onecode section executable by a machine, thereby causing the machine toperform the steps as described above for a method and system for adistributed transceiver for high frequency applications.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method for processing communication signals, the method comprising:generating a second signal from a first signal by: frequency-translatingsaid first signal via a plurality of conversion stages, wherein: each ofsaid plurality of conversion stages frequency-translates a correspondinginput signal by a local oscillator frequency or by a fraction of saidlocal oscillator frequency, and each of said plurality of conversionstages comprises a multiplier and a notch filter; and said first signalis said corresponding input signal to an initial stage of a saidplurality of conversion stages, an output signal of a previous one ofsaid plurality of conversion stages is said corresponding input signalto a subsequent one of said plurality of conversion stages, and saidsecond signal is an output signal of a final stage of said plurality ofconversion stages.
 2. The method according to claim 1, wherein saidplurality of conversion stages are communicatively coupled in a cascadeconfiguration.
 3. The method according to claim 1, wherein said firstsignal is a radio frequency signal or an intermediate frequency signaland said second signal is a baseband signal.
 4. The method according toclaim 1, wherein said first signal is a radio frequency signal or abaseband signal and said second signal is an intermediate frequencysignal.
 5. The method according to claim 1, wherein said first signal isa baseband signal or an intermediate frequency signal and said secondsignal is a radio frequency signal.
 6. The method according to claim 1,comprising generating a fractional local oscillator signal associatedwith said fractional local oscillator frequency from a local oscillatorsignal by using one or more frequency dividers.
 7. The method accordingto claim 1, comprising mixing a local oscillator signal and/or one ormore mixing signals to generate a fractional local oscillator signalassociated with said fractional local oscillator frequency.
 8. Themethod according to claim 7, comprising dividing said local oscillatorsignal via one or more frequency dividers to generate said one or moremixing signals.
 9. The method according to claim 1, wherein a localoscillator signal is a sinusoidal signal with a frequency equal to saidlocal oscillator frequency.
 10. The method according to claim 1, whereinsaid notch filter comprises one or more inductors and one or morecapacitors.
 11. The method according to claim 1, wherein said notchfilter comprises one or more microstrips.
 12. A system for processingcommunication signals, the system comprising: one or more circuits, saidone or more circuits enabled to generate a second signal from a firstsignal by: frequency-translating said first signal via a plurality ofconversion stages, wherein: each of said plurality of conversion stagesfrequency-translates a corresponding input signal by a local oscillatorfrequency or by a fraction of said local oscillator frequency, and eachof said plurality of conversion stages comprises a multiplier and anotch filter; and said first signal is said corresponding input signalto an initial stage of a said plurality of conversion stages, an outputsignal of a previous one of said plurality of conversion stages is saidcorresponding input signal to a subsequent one of said plurality ofconversion stages, and said second signal is an output signal of a finalstage of said plurality of conversion stages.
 13. The system accordingto claim 12, wherein said plurality of conversion stages arecommunicatively coupled in a cascade configuration.
 14. The systemaccording to claim 12, wherein said first signal is a radio frequencysignal or an intermediate frequency signal and said second signal is abaseband signal.
 15. The system according to claim 12, wherein saidfirst signal is a radio frequency signal or a baseband signal and saidsecond signal is an intermediate frequency signal.
 16. The systemaccording to claim 12, wherein said first signal is a baseband signal oran intermediate frequency signal and said second signal is a radiofrequency signal.
 17. The system according to claim 12, wherein said oneor more circuits generate a fractional local oscillator signalassociated with said fractional local oscillator frequency from a localoscillator signal by using one or more frequency dividers.
 18. Thesystem according to claim 12, wherein said one or more circuits mix alocal oscillator signal and/or one or more mixing signals to generate afractional local oscillator signal associated with said fractional localoscillator frequency.
 19. The system according to claim 18, wherein saidone or more circuits dived said local oscillator signal via one or morefrequency dividers to generate said one or more mixing signals.
 20. Thesystem according to claim 12, wherein a local oscillator signal is asinusoidal signal with a frequency equal to said local oscillatorfrequency.
 21. The system according to claim 12, wherein said notchfilter comprises one or more inductors and one or more capacitors. 22.The system according to claim 12, wherein said notch filter comprisesone or more microstrips.